Sub sea hybrid valve actuator system and method

Abstract

A sub sea valve actuator system including a piston and cylinder assembly and a return spring arranged in an actuator housing, a hydraulic pump and electric motor assembly associated with the piston and cylinder assembly, and hydraulic flow lines for hydraulic medium driving the piston and cylinder in relative displacement against a force of the return spring. The valve actuator system includes a detector configured to detect an end-of-stroke position of the piston and cylinder assembly. The detector includes at least one of: a motor current monitoring circuit unit, a hydraulic medium pressure sensor unit, a position sensor unit, and a linear variable differential transformer unit. An electromechanical arresting mechanism is arranged to be energized for releasably arresting the return spring in a compressed state in result of the detected end-of-stroke position. A method for operation of a sub sea valve actuator system by which an end-of-stroke position for a piston and cylinder assembly in a sub sea valve actuator system can be determined.

The invention claimed is: 
     
       1. A sub sea valve actuator system comprising:
 a piston; 
 a cylinder assembly; 
 a return spring; 
 an actuator housing in which the piston, the cylinder assembly and the return spring are arranged; 
 a hydraulic pump; 
 an electric motor assembly, wherein the hydraulic pump and the electric motor are associated with the piston and cylinder assembly; 
 hydraulic flow lines for hydraulic medium driving the piston and cylinder in relative displacement against a force of the return spring; 
 a detector arranged to detect an end-of-stroke position of the piston and cylinder assembly, wherein said detector comprises at least one of: 
 a motor current monitoring circuit unit; 
 a hydraulic medium pressure sensor unit; 
 a position sensor unit; and 
 a linear variable differential transformer unit; and 
 an electromechanical arresting mechanism is arranged to be energized for releasably arresting the return spring in a compressed state in result of the detected end-of-stroke position. 
 
     
     
       2. The actuator system according to  claim 1 , further comprising:
 an electronics canister in which at least one of the motor current monitoring circuit unit and the pressure sensor unit is arranged, wherein the electronics canister is retrievably connected to the actuator housing. 
 
     
     
       3. The actuator system according to  claim 1 , wherein components of at least one of the position sensor unit and the linear variable differential transformer unit are arranged in the actuator housing. 
     
     
       4. The actuator system according to  claim 1 , further comprising:
 a logic unit configured to control the electromechanical arresting mechanism, wherein the motor current monitoring circuit unit is configured to transmit an end-of-stroke signal to the logic unit to hold the valve in production mode against the force of the return spring. 
 
     
     
       5. The actuator system according to  claim 1 , further comprising:
 a logic unit configured to control the electromechanical arresting mechanism, wherein the pressure sensor unit is configured to generate a pressure signal in the unit to hold the valve in production mode against the force of the return spring. 
 
     
     
       6. The actuator system according to  claim 1 , further comprising:
 a logic unit configured to control the electromechanical arresting mechanism, wherein at least one of the position sensor unit and the linear variable differential transformer unit is configured to transmit an end-of-stroke signal to the logic unit to hold the valve in production mode against the force of the return spring. 
 
     
     
       7. The actuator system according to  claim 1 , further comprising:
 a hydraulic power unit retrievably connected to the actuator housing, wherein the hydraulic pump and electrical motor assembly are arranged in the hydraulic power unit. 
 
     
     
       8. The actuator system according to  claim 7 , further comprising:
 a reversible, fixed displacement hydraulic pump configured to supply hydraulic medium to the piston and cylinder assembly. 
 
     
     
       9. The actuator system according to  claim 8 , further comprising:
 a flow line opening in an end of the piston, wherein hydraulic medium is supplied via the flow line opening wherein the piston is stationary in the actuator housing. 
 
     
     
       10. The actuator system according to  claim 9 , further comprising:
 a return flow line, wherein the cylinder is arranged displaceable on the piston in the actuator housing filled with hydraulic medium communicating with the hydraulic pump via the return flow line. 
 
     
     
       11. The actuator system according to  claim 9 , wherein the actuator housing comprises a stem projecting from the cylinder in a forward direction, and a locking bolt projecting from the cylinder in an aft direction, wherein the locking bolt extends through the piston to be releasably engaged, in the end-of-stroke position of the cylinder, by locking dogs arranged pivotally in the actuator housing. 
     
     
       12. The actuator system according to  claim 11 , further comprising:
 an electromagnet/solenoid or a shape memory alloy device, wherein the locking dogs are controllable into locking engagement with the locking bolt upon energizing an the electromagnet/solenoid or the shape memory alloy device. 
 
     
     
       13. A method for operation of a sub sea valve actuator system, comprising a piston and cylinder assembly and a return spring arranged in an actuator housing, a hydraulic pump and electric motor assembly associated with the piston and cylinder assembly, hydraulic flow lines for hydraulic medium driving the piston and cylinder in relative displacement against the force of the return spring, the method comprising:
 arranging an electromechanical arresting mechanism effective for releasably arresting the return spring in a compressed state; 
 determining an end-of-stroke position of the piston and cylinder assembly through at least one of: 
 detecting a current supplied to/consumed by the electric motor; 
 detecting a pressure in the hydraulic medium; 
 detecting a position of the piston relative to the cylinder; and 
 detecting an absolute position of the piston or the cylinder; and 
 energizing the electromechanical arresting mechanism in result of the detected end-of-stroke position of the piston and cylinder assembly. 
 
     
     
       14. The method according to  claim 13 , further comprising:
 powering the electric motor at standstill in the end-of-stroke position while detecting at least one of the motor current consumption, the hydraulic medium pressure, the position of the piston relative to the cylinder, and the absolute position of the piston or the cylinder, and discontinuing the power supply to the electric motor upon detection of the end-of-stroke position of the piston and cylinder assembly. 
 
     
     
       15. The method according to  claim 14 , further comprising:
 activating the electromechanical arresting mechanism upon passage of a certain delay in time during which the electric motor is stalled at full torque. 
 
     
     
       16. The method according to  claim 14 , further comprising:
 accelerating the electric motor at minimum torque provided from a spring charged accumulator arranged in the flow of hydraulic medium from the pump to the cylinder. 
 
     
     
       17. The method according to  claim 13 , further comprising:
 arranging at least one of a motor current monitoring circuit unit and a hydraulic medium pressure sensor unit in a separate retrievable electronics canister which is connectable to the actuator housing. 
 
     
     
       18. The method according to  claim 13 , further comprising:
 arranging components of at least one of a position sensor unit and a linear variable differential transformer unit in the actuator housing. 
 
     
     
       19. The method according to  claim 13 , further comprising:
 assembling the hydraulic pump and the electrical motor in a hydraulic power unit which is retrievably connected to the actuator housing.